Physics and Astronomy

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This is the collection for the University of Waterloo's Department of Physics and Astronomy.

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Browsing Physics and Astronomy by Author "Budakian, Raffi"

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    Growth of Silicon Nanowire Mechanical Oscillators for Force-Detected Magnetic Resonance Measurements
    (University of Waterloo, 2018-01-19) Liu, Xudong; Budakian, Raffi
    This thesis describes two ways to grow silicon nanowires with the catalyst gold (Au) by Chemical Vapor Deposition (CVD) system. One way to prepare catalyst is drop-casting gold nanoparticles solution, the other is making a gold pattern by electron beam lithography (EBL). The diameters of silicon nanowires can be controlled by size of gold nanoparticles in the solution or the size of gold nano-disks which is achieved by EBL. The position-controlled epitaxial growth of Si nanowires is realized by gold nano-disks pattern through EBL. Our Si nanowires are grown on the n-type Si (111) wafer at the same condition. The length is 12-17 μm for Si nanowires 50-150nm in diameter. The taper of Si nanowires is 1 nm/μm in both ways. We found that the growth rates are depend on the size of Si nanowires in drop-casting method, but independent in EBL method. Our purpose of growing Si nanowires is to use it as a cantilever in magnetic resonance force microscopy (MRFM) due to its high aspect ratio and low mechanical dissipation. Therefore, the Si nanowires is required to be vertical and smooth. A high vertical yield, 80%, is achieved by our growth recipe. With HCl added, the surface of Si nanowire is polished. Moreover, the lowest intrinsic dissipation of our nanowire is 6×〖10〗^(-15) kg/s at room temperature, and our Si nanowires can be used as a force sensor for MRFM.
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    Nanoscale Dynamic Nuclear Polarization in Force-Detected Magnetic Resonance
    (University of Waterloo, 2024-08-13) Singh, Namanish; Budakian, Raffi
    Nuclear magnetic resonance (NMR) has played a pivotal role in modern science with its ability to perform non-destructive imaging and spectroscopy of various systems. Despite this, NMR has been plagued by low detection sensitivity when trying to study nanoscale ensembles of spins, primarily due to the small thermal polarization of nuclear spins. Extending the capabilities of NMR to address nanoscale sample volumes would present exciting opportunities for studying biological systems, enabling high-resolution imaging of single biomolecules and virus particles. Over the years, a great deal of techniques to improve the detection sensitivity of the measurement apparatus have been made. Force-detected magnetic resonance is one such technique, that has demonstrated the capability to detect nanoscale ensembles of spins, where it has been successfully used to achieve three dimensional images of virus particles. Nevertheless, further improvements are needed to achieve high resolution atomic scale imaging of nanoscale systems. Techniques such as dynamic nuclear polarization (DNP) have been widely implemented in traditional NMR experiments for boosting the signal, by transferring the comparatively larger polarization of electrons to surrounding nuclei . The use of DNP in force-detected magnetic resonance platforms however, has remained relatively limited though. Bringing DNP to nanoscale force-detected magnetic resonance setups would mark a significant next step in improving the detection sensitivity of nanoscale NMR experiments. In this thesis, we discuss the implementation of DNP in a force-detected magnetic resonance experiment in order to achieve sensitivities needed to realize high resolution imaging of nanoscale spin ensembles. In these experiments, we observed a 100 fold enhancement in the proton thermal signal in a nanoscale droplet composed of trityl-OX063 radicals suspended in a sugar-water glassy matrix. We also compare the signal-to-noise ratio (SNR) boost this provides over measurements that rely upon statistical polarization, where we demonstrate a reduction in averaging time by a factor of 204. This work explores various tunable parameters to optimize the enhancement such as the proton and radical relaxation times. This work also investigates the role fast-relaxing paramagnetic defect centers from the surrounding environment play in reducing the radicals spin-lattice relaxation time, a crucial component for efficient DNP.
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    Numerical Engineering of Adiabatic Quantum Operations
    (University of Waterloo, 2020-01-23) Tabatabaei, Seyed Sahand; Budakian, Raffi
    Adiabatic quantum operations are ubiquitous in fields such as quantum information processing, quantum control, and magnetic resonance, where their high fidelity and general robustness renders them an essential tool for various applications. This inherent robustness due to adiabaticity can, however, be impaired in cases where the experimental conditions strictly require very fast evolution times. In this thesis, we provide a gradient-based numerical optimization protocol for efficiently engineering adiabatic operations, allowing for the systematic inclusion of robustness criteria against various experimental non-idealities, including inhomogeneities and uncertainties in system parameters, as well as perturbations in the Hamiltonian such as spin-spin interactions. The protocol is implemented in the context of adiabatic passages for magnetic resonance, and it is shown that in addition to conventional adiabatic pulses, it can also generate exceptionally fast operations that although slightly deviate from adiabaticity in limited instances, still lead to a high fidelity. The effectiveness of our method for addressing perturbations is also demonstrated by designing a fast adiabatic passage for dipolar-coupled electrons, and numerically comparing its performance with a pulse without such considerations.
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    Ultra Low Dissipation Silicon Nanowire Resonator Arrays for Scanning Probe Applications
    (University of Waterloo, 2020-01-23) Jordan, Andrew; Budakian, Raffi
    This work describes the fabrication and characterization of silicon nanowire oscillators for use in ultra-high sensitivity force detection. These structures are optimized for use as scanning probes by fabricating them at the edge of a chip, allowing for easy optical displacement detection. Two sets of nanowire samples are described, with mean diameters of 132 nm and 77 nm. The characterization of the mechanical properties of the nanowire, such as quality factor and resonant frequency, is done by optical interferometry. The thermomechanical noise-limited force sensitivity of these nanowires is recorded across a range of temperatures and reaches as low as 500±20 zN Hz^-1/2 at 4.2 K.